Washing machine and control method thereof

ABSTRACT

A washing machine includes a drum accommodating laundry, a motor configured to rotate the drum, a speed sensor configured to detect a rotational speed of the drum, and a processor. The processor configured to: determine a mass of the laundry corresponding to each of a first acceleration section and a second acceleration section based on the rotational speed detected by the speed sensor, and control the motor such that an absolute value of the rotational speed at a start time of the first acceleration section is substantially the same as an absolute value of a rotational speed at a start time of the second acceleration section. A rotational direction of the drum corresponding to the rotational speed at the start time of the first acceleration section is opposite to a rotational direction of the drum corresponding to the rotational speed at the start time of the second acceleration section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. 119 to Korean Patent Application No. 10-2020-0026081, filed on Mar. 2, 2020, in the Korean Intellectual Property Office, which claims the benefit of Japanese Patent Application No. 2019-061480 filed on Mar. 27, 2019, in the Japan Patent Office, the disclosures of which are herein incorporated by reference in their entireties.

BACKGROUND 1. Field

The disclosure relates to a washing machine configured to determine a mass of laundry.

2. Description of Related Art

Techniques for obtaining the mass of laundry in a washing machine are known. When the mass of laundry is obtained, washing time, quantity, etc. may be changed based on the obtained mass of the laundry. For example, Patent Document 1 discloses a technique that detects the mass of laundry based on rise time and fall time of a rotational speed of a motor.

RELATED ART DOCUMENT Patent Document

(Patent Document 1) JP2002126390 A

SUMMARY

Therefore, it is an aspect of the disclosure to provide a washing machine capable of more accurately measuring a mass of laundry even when an imbalance of laundry occurs.

Additional aspects of the disclosure will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the disclosure.

In accordance with an aspect of the disclosure, a washing machine includes a drum in which laundry is accommodated, a motor configured to rotate the drum, a speed sensor configured to detect a rotational speed of the drum, and at least one processor configured to determine a mass of the laundry corresponding to each of a first acceleration section and a second acceleration section based on the rotational speed detected by the speed sensor, and configured to control the motor wherein an absolute value of a rotational speed at a start time of the first acceleration section is substantially the same as an absolute value of a rotational speed at a start time of the second acceleration section and a direction of the rotational speed at, the start d me of the first acceleration section is opposite to a direction of the rotational speed at the start time of the second acceleration section.

Before the start time of the first acceleration section, the at least one processor may allow the motor to drive at the substantially the same rotational speed in a first constant speed section, and before the start time of the second acceleration section, the at least one processor may, allow the motor to drive at the substantially the same rotational speed in the first constant speed section.

A position of the laundry at the start time of the first acceleration section may be different by 180 degrees from a position of the laundry at the start time of the second acceleration section with respect to a center of the drum.

The at least one processor may allow the drum to rotate an integer number of times in the first and second acceleration sections.

The at least one processor may determine the mass of the laundry based on the mass detected in each of the first acceleration section and the second acceleration section.

The at least one processor may determine the mass of the laundry based on an average of the mass detected in the first acceleration section and the second acceleration section.

The at least one processor may determine the start time of the first acceleration section and the start time of the second acceleration section based on a rotation angle of the drum.

Based on (n+0.5) rotation (n: natural number) of the motor, the at least one processor may determine a difference between the rotation angle at the start time of the first acceleration section and the rotation angle at the start time of the second acceleration section.

The at least one processor may determine the start time of the first acceleration section and the start time of the second acceleration section based on at least one of the rotational speed, a current flowing in the motor, and a voltage applied to the motor.

A phase difference of one of the rotational speed of the motor, the current flowing in the motor, and the voltage applied to the motor corresponding to the start time of the first acceleration section and the start time of the second acceleration section may be 180 degrees.

In a continuous driving of the drum, the at least one processor may perform the first acceleration section and the second acceleration section, and may allow the rotational speed of the motor to be substantially 30 revolutions per minute (rpm) or more between the first acceleration section and the second acceleration section.

The at least one processor may allow the rotational speed of the motor to be substantially 300 rpm or less at an end time of the first and second acceleration sections.

An angle of a rotation axis of the drum with respect to a horizontal direction may be from 0 (zero) degree to 45 degrees.

In accordance with another aspect of the disclosure, a control method of a washing machine includes detecting a rotational speed of a drum in which laundry is accommodated, determining a mass of the laundry corresponding to each of a first acceleration section and a second acceleration section based on the detected rotational speed, and controlling the motor configured to the drum wherein an absolute value of a rotational speed at a start time of the first acceleration section is substantially the same as an absolute value of a rotational speed at a start time of the second acceleration section and a direction of the rotational speed at the start time of the first acceleration section is opposite to a direction of the rotational speed at the start time of the second acceleration section.

The controlling may include allowing the motor to drive at the substantially the same rotational speed in a first constant speed section before the start time of the first acceleration section, and allowing the motor to drive at the substantially the same rotational speed in the first constant speed section before the start time of the second acceleration section.

The controlling may include allowing a position of the laundry at the start time of the first acceleration section to be different by 180 degrees from a position of the laundry at the start time of the second acceleration section with respect to a center of the drum.

The controlling may include allowing the drum to rotate an integer number of times in the first and second acceleration sections.

The determining of the mass may include determining the mass of the laundry based on the mass detected in each of the first acceleration section and the second acceleration section.

The determining of the mass may include determining the mass of the laundry based on an average of the mass detected in the first acceleration section and the second acceleration section.

The controlling may include determining the start time of the first acceleration section and the start time of the second accelerationsection based on a rotation angle of the drum.

Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely.

Moreover, various functions described below can be implemented or supported by one or more computer programs, each of which is formed from computer readable program code and embodied in a computer readable medium. The terms “application” and “program” refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer readable program code. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. A “non-transitory” computer readable medium excludes wired, wireless, optical, or other communication links that transport transitory electrical or other signals. A non-transitory computer readable medium includes media where data can be permanently stored and media where data can be stored and later overwritten, such as a rewritable optical disc or an erasable memory device.

Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects of the disclosure will become apparent and more readily appreciated from the following description of embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a view illustrating a structure of a washing machine according to an embodiment of the disclosure;

FIG. 2 is a view illustrating a profile of intermittent driving of a motor for obtaining a mass of laundry according to an embodiment of the disclosure;

FIG. 3 is a view illustrating a profile of intermittent driving of the motor for obtaining a mass of laundry according to an embodiment of the disclosure;

FIG. 4 is a view illustrating an eccentric position due to uneven distribution of the laundry in a drum according to an embodiment of the disclosure; and

FIG. 5 illustrates a flow chart according to an embodiment of the disclosure.

DETAILED DESCRIPTION

FIGS. 1 through 5, discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device.

In the following descriptions and drawings, corresponding parts are represented by the same reference numerals. The sizes of the elements shown in the drawings are not necessarily drawn to scale.

FIG. 1 is a view illustrating a structure of a washing machine 100 according to an embodiment of the disclosure. The washing machine 100 includes a drum 110 in which laundry is accommodated, a motor 120 configured to rotate the drum 110, a controller 130 configured to control rotation of the motor 120, a sensor 140 configured to detect a rotational speed of the drum 110, and a processing portion 150.

Meanwhile, the controller 130 and the processing portion 150 may be implemented with at least one processor.

According to an embodiment, the sensor 140 detects a rotation angle of the drum 110 in addition to the rotational speed of the drum 110. The processing portion 150 may determine the mass of the laundry based on the rotational speed in first and second acceleration sections to be described later.

In various embodiments, the rotational speed of the drum 110 is used. The sensor 140 is a position sensor configured to directly detect the rotational speed of the drum 110, but is not limited thereto. Therefore, the sensor 140 may be any suitable sensor.

The processing portion 150 may typically include at least one processor 152 and a memory 154. The processor 152 executes a computer program configured to process of controlling the rotation of the drum 110 and the motor 120 and configured to process of obtaining the mass of the laundry. The memory 154 typically stores such computer programs and associated data. The processor 152 outputs a signal for controlling the rotation of the motor 120 to the controller 130. The controller 130 drives the motor 120 based on the control signal from the processor 152. FIG. 1 illustrates that the controller 130 and the processing portion 150 are separate functional blocks, but may be implemented as a single functional block.

FIG. 2 is a view illustrating a profile 200 of intermittent driving of the motor 120 for obtaining a mass of laundry according to an embodiment of the disclosure. In FIG. 2, a horizontal axis represents the time, and a vertical axis represents the rotational speed of the drum 110. The profile 200 includes a first constant speed section 211, a first acceleration section 212, a stop section 215, a second constant speed section 221, and a second acceleration section 222. A sign of the rotational speed indicates a rotational direction of the drum 110. Therefore, from time 0 (zero) to the stop section 215, the drum 110 rotates in one direction, and thereafter rotates in the opposite direction.

According to an embodiment, the controller 130 controls the rotation of the motor 120 to allow an absolute value of the rotational speed of the drum 110 at the start of the first acceleration section 212 to be the same as an absolute value of the rotational speed of the drum 110 at the start of the second acceleration section 222 and to allow sings thereof to be opposite to each other.

FIG. 3 is a view illustrating a profile 300 of intermittent driving of the motor 120 for obtaining a mass of laundry according to an embodiment of the disclosure. In FIG. 3, a horizontal axis represents the time, and a vertical axis represents the rotational speed of the drum 110. The profile 300 includes a first constant speed section 311, a first acceleration section 312, a second constant speed section 321, and a second acceleration section 322. Unlike the profile 200, the profile 300 does not include a stop section.

According to an embodiment, the constant speed section, the acceleration section, and the deceleration section may be provided prior to the first constant speed section 311. Accordingly, a position of the laundry in the drum 110 may be fixed in advance.

According to an embodiment, the controller 130 controls the rotation of the motor 120 to provide the first constant speed section 311, in which the rotational speed of the drum 110 is constant, prior to the first acceleration section 312 and to provide the second constant speed section 321, in which the rotational speed of the drum 110 is constant, prior to the second acceleration section 322.

FIG. 4 is a view illustrating an eccentric position due to uneven distribution of the laundry in the drum 110 according to an embodiment of the disclosure. The drum 110 rotates about a rotation axis 410. Laundry 420 in the drum 110 may have an uneven distribution as illustrated in FIG. 4.

At this time, a center 430 of the drum 110 is also shifted from the rotation axis 410 due to the uneven distribution of the laundry 420. When it is assumed that a line, which is along the rotation axis 410 and then intersects a plane corresponding to an opening portion of the drum 110 perpendicular to the rotation axis 410, is a reference line 440, an angle of the center 430 with respect to the reference line 440 corresponds to an eccentric position 450 caused by the uneven distribution of the laundry 420 in the drum 110. The eccentric position 450 may be set in a range of 0 to 360 degrees. In the disclosure, the position of the drum 110 is represented by the eccentric position 450, which may be named as a phase.

According to an embodiment using the profile 200 (intermittent driving) or the profile 300 (continuous driving), a start time of the first acceleration section and the second acceleration section corresponds to two points in which the eccentric position 450 caused by the uneven distribution of the laundry 420 in the drum 110 is shafted by 180 degrees. In an embodiment using the profile 300 (continuous driving), as shown in FIG. 3, the eccentric position 450 at a start time of the first acceleration section 312 is 270 degrees, and the eccentric position 450 at a start time of the second acceleration section 322 is 90 degrees. Therefore, the start time of the first acceleration section 312 and the second acceleration section 322 corresponds to the two points in which the eccentric position 450 caused by the uneven distribution of the laundry 420 in the drum 110 is shafted by 180 degrees. In another embodiment using the profile 200 (intermittent driving), a start time of the first acceleration section 212 and the second acceleration section 222 corresponds to two points in which the eccentric position 450 caused by the uneven distribution of the laundry 420 in the drum 110 is shafted by 180 degrees.

In an embodiment using the profile 200 (intermittent driving) or the profile 300 (continuous driving), the drum 110 rotates n times (n: natural number) in the first acceleration section and the second acceleration section. For example, in an embodiment, the drum 110 rotates once in the first acceleration section 312 and the second acceleration section 322, but it is not limited thereto. Therefore, as long as the number of rotation of the drum 110 in the first acceleration section 312 is the same as the number of rotation of the drum 110 in the second acceleration section 322, the drum 110 may rotate n times (n: natural number) other than once. “The number of rotation” of the drum represents the number of times in which the drum rotates. For example, the drum 110 may rotate two times in the first acceleration section 312 and the second acceleration section 322.

In an embodiment using the profile 200 (intermittent driving) or the profile 300 (continuous driving), the processing portion 150 obtains the mass based on the mass detected in the first and second acceleration sections. When a torque of the motor 120 is constant, the acceleration in the first and second acceleration sections depends on the mass of the laundry 420.

For example, when the mass of the laundry 420 is heavy, the increase in the rotational speed of the drum 110 is small even when the drum 110 accelerates in the acceleration section. However, when the mass of the laundry 420 is light, the increase in the rotational speed of the drum 110 increases based on the acceleration of the drum 110 in the acceleration section. Therefore, the processing portion 150 may obtain the mass of the laundry 420 based on the increase amounts of the two rotational speeds in the first and second acceleration sections.

In an embodiment using the profile 200 and the profile 300, an angle of the rotation axis of the drum 110 of the washing machine 100 according to the disclosure with respect to the horizontal direction is from 0 (zero) degree to 45 degrees. In this range, it is possible to effectively obtain the mass of the laundry 420 from two mass values based on the acceleration of the first acceleration section 312 and the second acceleration section 322. A washing machine operated in this range includes a washing machine that is commonly referred as “a drum type washing machine”. In the drum type washing machine, the rotation axis of the drum 110 is relatively close to the horizontal direction. Accordingly, due to the gravity, the rotational speed may be reduced when the eccentric position 450 moves up and the rotational speed may be increased when the eccentric position 450 moves down. Even when such a variation in the rotational speed occurs, it is possible to obtain a value closer to the true mass of the laundry 420 based on the two mass values of the laundry 420 obtained separately in the first acceleration section and the second acceleration section, which will be described later.

In the example of FIG. 3, because the start time of the first acceleration section 312 and the second acceleration section 322 corresponds to the two points in which the eccentric position 450 caused by the uneven distribution of the laundry 420 in the drum 110 is shafted by 180 degrees, it is possible to reduce an error that may occur when detecting the mass of the laundry 420. This effect is also obtained in the example of FIG. 2. It is appropriate to determine the mass of the laundry 420 based on an average of two masses detected in the first and second acceleration sections. Accordingly, the processing portion may more reduce the error that may occur when detecting the mass of the laundry 420.

By the continuous driving of the profile 300, it is possible to detect the mass two times while maintaining the arrangement of the laundry 420 in the drum 110 that is maintaining the eccentric position and the imbalance.

The imbalance is a parameter determined by a weight corresponding to the uneven distribution of the laundry 420 in the drum 110 and a distance of the laundry 420 from the rotation axis 410. As the weight and the distance are increased, the imbalance may be increased. When the rotation direction is changed as illustrated in the profile 200, a stop section of the motor 120 is generated. In the stop section, the centrifugal force is lost, and the laundry 420 attached to the side of the drum 110 falls down in the vertical direction and thus the arrangement of the laundry 420 may be changed.

At this time, the eccentric position and the unbalance amount change. The eccentric position is corrected by monitoring the phase of the rotational speed or the like, but the imbalance is not corrected. Therefore, the profile 200 has a larger deviation than the profile 300.

Accordingly, the profile 300 is more appropriate than the profile 200.

In an embodiment using the profile 300, the first acceleration section 312 and the second acceleration section 322 are generated during continuous driving of the drum, and the rotational speed of the drum is maintained at 30 rpm or more in the first acceleration section 312 and the second acceleration section 322.

“Rpm” may mean revolutions per minute of the motor and the drum.

Accordingly, the movement of the laundry 420 in the drum 110 may be reduced between the first acceleration section 312 and the second acceleration section 322.

As a result, the error at the detection of the mass of the laundry 420 may be reduced.

As mentioned above, the start time of the first acceleration section (for example 312) and the second acceleration section (for example 322) corresponds to the two points in which the eccentric position 450 caused by the uneven distribution of the laundry 420 in the drum 110 is shafted by 180 degrees. Therefore, it can be detected that the phase of the eccentric position 450 is shifted by 180 degrees at the start time of the first acceleration section and the second acceleration section.

According to an embodiment, the processing portion 150 obtains the two points, in which the phase is shifted by 180 degrees, based on the rotation angle of the drum 110.

The rotation angle of the drum 110 may be detected by the sensor 140. More particularly, the difference between the rotation angle of the two points, in which the phase is shifted by 180 degrees, corresponds to (n+0.5) rotation (n: natural number).

The phase detection of the start time based on the rotation angle may be performed in such a way that an angle at the start time of the first acceleration section is stored and then the second acceleration section starts at a timing in which the rotation angel is shafted by 180 degrees from the stored angle.

The phase detection of the start time based on the rotation angle is more accurately performed in the embodiment using the profile 300 (continuous driving).

According to an embodiment, the processing portion 150 obtains the two points, in which the phase is shifted by 180 degrees, based on at least one of the rotational speed of the drum 110, a current flowing in the motor 120, and a voltage applied to the motor 120. More particularly, in the two points in which the phase is shifted by 180 degrees, a phase difference of one of the rotational speed of the drum 110, the current flowing in the motor 120, and the voltage applied to the motor 120 is 180 degrees.

Due to the influence of the eccentric position 450 caused by the uneven distribution of the laundry 420 in the drum 110, the rotational speed of the drum is changed even in the constant speed section.

When the variation of the rotational speed is plotted with respect to the time axis, a sine wave shape may be generated. There is a correlation between the phase of the waveform and the eccentric position 450. Therefore, the eccentric position 450 may be obtained from the phase of the sine wave waveform indicating the variation of the rotational speed. As the uneven distribution of the laundry 420 in the drum 110 is reduced, the amplitude of the waveform is reduced and the phase detection is difficult.

However, when the uneven distribution is small, the uneven distribution has little effect on the mass detection. Therefore, even when the phase is not detected, there is little effect on the difference (i.e., deviation) of the mass detected in the two acceleration sections. By detecting the phase of the variation waveform of the rotational speed, the controller may start the second acceleration section at a timing that is shifted by 180 degrees from the start time of the first acceleration section.

In the same manner as the above mentioned variation of the rotational speed of the drum, the current flowing in the motor 120 and the voltage applied to the motor 120 also vary in the constant speed section. Therefore, by using any one of the current flowing in the motor 120 or the voltage applied to the motor 120, it is possible to detect the phase at the start time in the same manner. For example, the current flowing in the motor 120 and the voltage applied to the motor 120 may be detected by the controller 130.

As mentioned above, it is possible to obtain the mass of the laundry 420 based on the acceleration of the first and second acceleration sections. In an embodiment using the profile 200 (intermittent driving) and the profile 300 (continuous driving), it is appropriate that the rotational speed of the drum 110 at an end time of the first and second acceleration sections is 300 rpm or less in terms of the load of the motor 120. In this range, it is possible to effectively obtain the mass of the laundry 420 based on the acceleration of the first and second acceleration sections.

FIG. 5 illustrates a flow chart according to an embodiment of the disclosure.

Referring to FIG. 5, the sensor may detect the rotational speed of the drum (1001).

Meanwhile, the processor may control the drum by controlling the motor, and the drum may be driven in the first acceleration section (1002).

The processor may determine the mass of laundry corresponding to the first acceleration section (1003).

The processor may perform the second acceleration section by controlling the motor at a point shifted by 180 degrees from the phase of the laundry at the start time of the first acceleration section (1004).

The processor may determine the mass of the laundry corresponding to the second acceleration section (1005).

The processor may determine the final mass of the laundry based on an average of the mass of the laundry obtained in the first acceleration section and the mass of the laundry obtained in the second acceleration section (1006).

As is apparent from the above description, the washing machine may more accurately measure the mass of laundry even when an imbalance of laundry occurs.

Each of the various functions in the disclosure may be realized by a single element or may be realized by a plurality of elements. Conversely, multiple functions may be realized by a single element. Each function may be realized by hardware, software, or a combination of hardware and software. The flowchart in the disclosure includes a plurality of blocks. The processing of these blocks may be performed serially or in parallel. Also, the order of some blocks may be changed.

The apparatus and the subject of the method of the disclosure include a computer. When the computer executes the program, the main functions of the apparatus and the subject of method of the disclosure are realized. The computer has a processor operating according to the program as the main hardware configuration. The processor may be any type as long as the function can be realized by executing a program. The processor is composed of one or more electronic circuits including semiconductor integrated circuits (IC) or large scale integration (LSI). The plurality of electronic circuits may be integrated in one chip or may be provided in a plurality of chips. The plurality of chips may be integrated into one device or may be provided in the plurality of devices.

Although a few embodiments of the disclosure have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the claims and their equivalents.

DESCRIPTION OF SYMBOLS

-   -   100: washing machine     -   110: drum     -   120: motor     -   130: controller     -   140: sensor     -   150: processing portion     -   152: processor     -   154: memory

Although the present disclosure has been described with various embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims. 

What is claimed is:
 1. A washing machine comprising a drum in which laundry is accommodated; a motor configured to rotate the drum; a speed sensor configured to detect a rotational speed of the drum; and a processor configured to: identify a mass of the laundry corresponding to each of a first acceleration section and a second acceleration section based on the rotational speed detected by the speed sensor, and control the motor such that an absolute value of the rotational speed at a start time of the first acceleration section is substantially the same as an absolute value of the rotational speed at a start time of the second acceleration section, wherein a rotational direction of the drum corresponding to the rotational speed at the start time of the first acceleration section is opposite to a rotational direction of the drum corresponding to the rotational speed at the start time of the second acceleration section.
 2. The washing machine of claim 1, wherein: before the start time of the first acceleration section, the processor is further configured to control the motor to drive at substantially the same rotational speed in a first constant speed section, and before the start time of the second acceleration section, the processor is further configured to control the motor to drive at substantially the same rotational speed in the first constant speed section.
 3. The washing machine of claim 1, wherein a position of the laundry at the start time of the first acceleration section is different by 180 degrees with respect to a center of the drum from a position of the laundry at the start time of the second acceleration section.
 4. The washing machine of claim 3, wherein the processor is further configured to control the drum to rotate an integer number of times in the first and second acceleration sections.
 5. The washing machine of claim 4, wherein the processor is further configured to identify the mass of the laundry based on the mass detected in each of the first acceleration section and the second acceleration section.
 6. The washing machine of claim 5, wherein the processor is further configured to identify the mass of the laundry based on an average of the mass detected in the first acceleration section and the second acceleration section.
 7. The washing machine of claim 1, wherein the processor is further configured to identify the start time of the first acceleration section and the start time of the second acceleration section based on a rotation angle of the drum.
 8. The washing machine of claim 7, wherein, based on a half of a rotation of the motor, the processor is further configured to identify a difference between the rotation angle at the start time of the first acceleration section and the rotation angle at the start time of the second acceleration section.
 9. The washing machine of claim 1, wherein the processor is further configured to identify the start time of the first acceleration section and the start time of the second acceleration section based on at least one of the rotational speed, a current flowing in the motor, or a voltage applied to the motor.
 10. The washing machine of claim 9, wherein a phase difference of one of the rotational speed of the motor, the current flowing in the motor, or the voltage applied to the motor corresponding to the start time of the first acceleration section and the start time of the second acceleration section is 180 degrees.
 11. The washing machine of claim 1, wherein, in a continuous driving of the drum, the processor is further configured to: perform the first acceleration section and the second acceleration section; and control the rotational speed of the motor to be substantially 30 revolutions per minute (rpm) or more in the first acceleration section and the second acceleration section.
 12. The washing machine of claim 1, wherein the processor is further configured to control the rotational speed of the motor to be substantially 300 rpm or less at an end time of the first and second acceleration sections.
 13. The washing machine of claim 1, wherein an angle of a rotation axis of the drum with respect to a horizontal direction is from 0 (zero) degree to 45 degrees.
 14. A control method of a washing machine comprising: detecting a rotational speed of a drum in which laundry is accommodated; identifying a mass of the laundry corresponding to each of a first acceleration section and a second acceleration section based on the detected rotational speed; and rotating the drum such that an absolute value of the rotational speed at a start time of the first acceleration section is substantially the same as an absolute value of the rotational speed at a start time of the second acceleration section, wherein a rotational direction of the drum corresponding to the rotational speed at the start time of the first acceleration section is opposite to a rotational direction of the drum corresponding to the rotational speed at the start time of the second acceleration section.
 15. The control method of claim 14, wherein the rotating further comprises: rotating the drum at substantially the same rotational speed in a first constant speed section before the start time of the first acceleration section; and rotating the drum at substantially the same rotational speed in the first constant speed section before the start time of the second acceleration section.
 16. The control method of claim 14, wherein the rotating further comprises rotating the drum such that a position of the laundry at the start time of the first acceleration section is different by 180 degrees with respect to a center of the drum from a position of the laundry at the start time of the second acceleration section.
 17. The control method of claim 16, wherein the rotating further comprises rotating the drum an integer number of times in the first and second acceleration sections.
 18. The control method of claim 17, wherein the identifying of the mass further comprises identifying the mass of the laundry based on the mass detected in each of the first acceleration section and the second acceleration section.
 19. The control method of claim 18, wherein the identifying of the mass further comprises identifying the mass of the laundry based on an average of the mass detected in the first acceleration section and the second acceleration section.
 20. The control method of claim 14, wherein the rotating further comprises identifying the start time of the first acceleration section and the start time of the second acceleration section based on a rotation angle of the drum. 